Aluminum alloy sheet and production method therefor

ABSTRACT

An aluminum alloy sheet according to the present disclosure includes 0.05 to 0.60% by mass of Si, 0.05 to 0.80% by mass of Fe, 0.05 to 0.25% by mass of Cu, 0.80 to 1.50% by mass of Mn, 0.80 to 1.50% by mass Mg, Al, and inevitable impurities. In this aluminum alloy sheet, a 45° caring ratio of a cup formed by a first drawing of the aluminum alloy sheet is 2.0% or less, and a value obtained by subtracting the 45° caring ratio from a 0-180° caring ratio of the cup formed by the first drawing of the aluminum alloy sheet is −1.0% or more and 2.0% or less.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a Section 371 National Stage Application of International Application No. PCT/JP2018/003495, filed Feb. 1, 2018, and published as WO 2018/143376 A1, on Aug. 9, 2018and claims the benefit of Japanese Patent Application No. 2017-16759 filed with the Japan Patent Office on Feb. 1, 2017, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an aluminum alloy sheet and a production method therefor.

BACKGROUND ART

Aluminum alloy sheets for can bodies obtained by a drawing and ironing (DI) formation are used for beverage cans and the like. The aluminum alloy sheets for can bodies obtained by the DI formation are generally produced by sequentially performing homogenizing treatment, hot rolling, and cold rolling on aluminum alloy ingots defined in JIS 3004 or JIS 3104. After the cold rolling, the aluminum alloy sheets are further subjected to, if necessary, degreasing and washing, applying a lubricant for cupping, and so on.

An earing ratio is a rate of a variation (earing) between projecting portions and depressed portions, formed in the peripheral of a rolled circular sheet when the rolled circular sheet is drawn into a cup-like shape, relative to the height of the cup. A high earing ratio causes various problems. Such problems include: (1) a problem of causing pinholes and tear-off (body cracking) during ironing due to chips exfoliating from the tips of the ears during formation of the cup; (2) a problem in which the dimensional accuracy of the can is decreased after a flange is formed; (3) a problem in which the amount of trimming after a can body is formed needs to be increased; and (4) a problem in which the depressed parts in the peripheral of the can cannot be completely removed by trimming.

Moreover, since recent cans have reduced diameters, ears may be formed even after necking. This has created a new problem in that these ears cause a variation in length of the flange in a subsequent flange processing, and thus seaming of the can body with a can-lid cannot be performed well.

The degree of the earing ratio in the aluminum alloy sheet is influenced by crystallographic anisotropy of the aluminum alloy sheet. More specifically, the earing ratio becomes small in a case where recrystallized texture components (0-90° ears) in a cube orientation formed after the hot rolling finishes, and rolled texture components (45° ears) formed by the cold rolling exist in good balance. Recently, to accommodate the reduction in diameter of can bodies, the degree of cold work is increased so as to strengthen the cans. Accordingly, the rolled texture components tend to increase. “0-90° ears” described above mean ears located at four angles 0°, 90°, 180°, and 270° relative to the rolling direction.

Patent Document 1 mentioned below proposes a method in which temperature conditions of, for example, homogenization and hot rolling are defined so as to control a dispersion state of precipitates so that recrystallized grains in the cube orientation are preferentially grown.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Unexamined Patent Application Publication No. H11-140576

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Due to the recent reduction in diameter of cans, it is strictly required to reduce the variation in length of flanges. It has been difficult in the conventional art to sufficiently reduce the variation in length of the flanges.

It is desirable, in one aspect of the present disclosure, to provide, an aluminum alloy sheet and a production method therefor that can reduce the variation in length of the flanges.

Means for Solving the Problems

One aspect of the present disclosure provides an aluminum alloy sheet comprising 0.05 to 0.60% by mass of Si, 0.05 to 0.80% by mass of Fe, 0.05 to 0.25% by mass of Cu, 0.80 to 1.50% by mass of Mn, 0.80 to 1.50% by mass of Mg, Al, and inevitable impurities. In this aluminum alloy sheet, a 45° earing ratio of a cup formed by a first drawing of the aluminum alloy sheet is 2.0% or less, and a value obtained by subtracting the 45° earing ratio from a 0-180° earing ratio of the cup formed by the first drawing of the aluminum alloy sheet is −1.0% or more and 2.0% or less. “0-180° earing ratio” described above means earing ratios at 0° and 180°.

The aluminum alloy sheet according to one aspect of the present disclosure can reduce the variation in length of a flange.

Another aspect of the present disclosure provides a production method for an aluminum alloy sheet. An aluminum alloy ingot contains 0.05 to 0.60% by mass of Si, 0.05 to 0.80% by mass of Fe, 0.05 to 0.25% by mass of Cu, 0.80 to 1.50% by mass of Mn, 0.80 to 1.50% by mass of Mg, Al, and inevitable impurities. The production method comprises homogenizing treatment, hot rough rolling with a reversing mill, hot finishing rolling with a tandem hot rolling machine, and cold rolling of the aluminum alloy ingot. The hot rough rolling with the reversing mill is performed under a condition where an ending temperature is 400 to 500° C., the reduction ratio at a last pass is 5 to 40%, a strain rate at the last pass is 5 to 30 s⁻¹. The cold rolling is performed under a condition where the reduction ratio is 80 to 90%.

The production method for an aluminum alloy sheet according to another aspect of the present disclosure can reduce the variation in length of the flange of the accordingly produced aluminum alloy sheet.

MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present disclosure will be described.

1. Aluminum Alloy Sheet (1) Components of Aluminum Alloy Sheet

An aluminum alloy sheet contains 0.05 to 0.60% by mass of Si, 0.05 to 0.80% by mass of Fe, 0.05 to 0.25% by mass of Cu, 0.80 to 1.50% by mass of Mn, 0.80 to 1.50% by mass of Mg, Al, and inevitable impurities.

Si induces a phase transformation of Al-Mn-Fe crystals to form harder Al-Mn-Fe-Si compounds. The Al-Mn-Fe-Si compounds have a solid lubricating effect. Formation of the Al-Mn-Fe-Si compounds improves ironing workability of the aluminum alloy sheet.

If the aluminum alloy sheet containing a suitable amount of Si is subjected to a drawing and ironing (DI) formation, a build-up caused by adhesion of an alloy die and a die can be inhibited.

If the Si content is 0.05% by mass or more, the effect to inhibit the aforementioned build-up is higher. Moreover, if the Si content is 0.05% by mass or more, it is not necessary to increase the purity of the aluminum metal so much. Accordingly, the costs required to prepare highly pure aluminum metal can be reduced, and thus a cost cut can be achieved.

If the Si content is 0.60% by mass or less, the earing ratio can be further decreased. The reasons are as follows. If the Si content is 0.60% by mass or less, precipitation of a fine a-AlMnFeSi phase during the hot rolling can be inhibited. The α-AlMnFeSi phase has an effect to inhibit recrystallization that takes place after the hot rolling finishes. Inhibiting the precipitation of the α-AlMnFeSi phase can facilitate the recrystallization after the hot rolling finishes, and can further reduce the earing ratio.

Fe facilitates crystallization of Mn and uniformly distributes the Mn crystals so as to improve the ironing workability of the aluminum alloy sheet. Fe improves the ironing workability because Fe forms compounds of Al-Mn-Fe, Al-Mn-Fe-Si, and so on that have the solid lubricating effect.

If the Fe content is 0.05% by mass or more, the ironing workability is further improved. Moreover, if the Fe content is 0.05% by mass or more, it is not necessary to increase the purity of the aluminum metal so much. Accordingly, the costs required to prepare highly pure aluminum metal can be reduced, and thus cost cut can be achieved.

If the Fe content is 0.80% by mass or less, it is possible to inhibit binding of Fe and Mn during melting and casting, and thus to inhibit formation of large primary crystal of Al-Mn-Fe compounds. This inhibits the large primary crystal of Al-Mn-Fe compounds from remaining in the aluminum alloy sheet after the rolling, and thus can inhibit cracks and pinholes from being formed in the DI formation.

Cu contributes to improve the strength of the aluminum alloy sheet. If the Cu content is 0.05% by mass or more, the strength of the aluminum alloy sheet is further improved. The further improvement in strength of the aluminum alloy sheet can provide sufficient buckling pressure for the DI formation.

If the Cu content is 0.25% by mass or less, an excessive increase in strength of the aluminum alloy sheet can be inhibited. This can further improve the ironing workability of the aluminum alloy sheet.

Mn is an element that contributes to improve the strength of the aluminum alloy sheet and to form the aforementioned crystals. Accordingly, Mn contributes to improve the ironing workability of the aluminum alloy sheet. If the Mn content is 0.80% by mass or more, the ironing workability of the aluminum alloy sheet is further improved. Moreover, if the Mn content is 0.80% by mass or more, the strength of the aluminum alloy sheet is further improved. The further improvement in strength of the aluminum alloy sheet can provide sufficient buckling pressure for the DI formation.

If the Mn content is 1.40% by mass or less, it is possible to inhibit the binding of Fe and Mn during the melting and casting, and thus to inhibit formation of the large primary crystal of Al-Mn-Fe compounds. This inhibits the large primary crystal of Al-Mn-Fe compounds from remaining in the aluminum alloy sheet after the rolling, and thus can inhibit cracks and pinholes from being formed in the DI formation.

Mg contributes to improve the strength of the aluminum alloy sheet. If the Mg content is 0.80% by mass or more, the strength of the aluminum alloy sheet is further improved. The further improvement in strength of the aluminum alloy sheet can provide sufficient buckling pressure for the DI formation.

If the Mg content is 1.50% by mass or less, the aluminum alloy sheet is less likely to be work-hardened. This renders formation of cracks less frequent during the ironing of the DI formation.

Al is the major component of the aluminum alloy sheet. Al is the balance of, for example, Si, Fe, Cu, Mn, Mg, and inevitable impurities in the aluminum alloy sheet.

(2) Regarding Earing Ratio

The earing ratio includes a 45° earing ratio of a cup formed by a first drawing, and a 0-180° earing ratio of the cup formed by the first drawing. These earing ratios affect the variation in length of the flange (flange width) (hereinafter also simply referred to as a flange length variation) of a can body produced by the DI formation and necking formation of the aluminum alloy sheet. The variation mentioned herein means the degree of difference in width of the flange of one can body at different positions.

If the 45° earing ratio of the cup formed by the first drawing is 2.0% or less, the flange length variation can be further reduced. If a value obtained by subtracting the 45° earing ratio from the 0-180° earing ratio is −1.0% or more, the flange length variation can be further reduced.

If the value obtained by subtracting the 45° earing ratio from the 0-180° earing ratio is 2.0% or less, it is possible to inhibit formation of pinholes and an occurrence of tear-off (body cracking) in the ironing that can be caused due to the 0-180° ears being overly extended and chips exfoliating from the tips of the ears during the formation of the drawn-and-ironed can.

When the can height of the can body, formed of the aluminum alloy sheet by the DI formation and the necking formation, is measured along its entire circumference, the difference between the maximum value and the minimum value of the can height is preferably 0.080 mm or smaller. In such a case, the flange length variation is limited, and thus the seaming of the can with a can-lid can be performed well. This difference between the maximum value and the minimum value is a neck height variation in Embodiments to be described below.

2. Production Method for Aluminum Alloy Sheet (1) Outline of Production Method

In the production method for an aluminum alloy sheet according to the present disclosure, homogenizing treatment, hot rough rolling with a reversing mill, hot finishing rolling with a tandem hot rolling machine, and cold rolling of the aluminum alloy ingot are performed.

(2) Aluminum Alloy Ingot

The aluminum alloy ingot can be produced through, for example, a direct chill casting method (semi-continuous casting method). The aluminum alloy ingot contains 0.05 to 0.60% by mass of Si, 0.05 to 0.80% by mass of Fe, 0.05 to 0.25% by mass of Cu, 0.80 to 1.50% by mass of Mn, 0.80 to 1.50% by mass of Mg, Al, and inevitable impurities. The composition of this ingot is, for example, identical to that of the above-described aluminum alloy sheet.

(3) Homogenizing Treatment

The homogenizing treatment is preferably performed, for example, at a temperature of 580 to 610° C. for 2 to 48 hours. If the temperature for the homogenizing treatment is at 580° C. or higher and the period of time is 2 hours or longer, homogenization can be sufficiently performed. As a result, the progress of the recrystallization, which takes place after the hot rolling finishes, is less likely to be inhibited, and 45° ears of the cold rolled sheet are inhibited from becoming too high.

If the temperature for the homogenizing treatment is 610° C. or lower, it is possible to inhibit an occurrence of a stripe-pattern defect (a defect called “flow marks”), which is visually observed on the outer surface of the lateral wall of the can after the DI formation. The flow marks are made due to bulges formed on the ingot surface and the defect due to the bulges remaining in a cold-rolled sheet. If the period of time for the homogenizing treatment is within 48 hours, the productivity of the aluminum alloy sheet is improved, and thus the production cost is reduced.

(4) Hot Rough Rolling

The ending temperature in the hot rough rolling is preferably, for example, 400 to 550° C. If the ending temperature is 400° C. or higher, the amount of rolled textures to be subjected to the hot finishing rolling is limited, and thus formation of 0-90° ears of the hot rolled sheet is inhibited. If the ending temperature is 550° C. or lower, oxidation of the surface of the hot rolled sheet and deterioration of the surface quality caused thereby can be inhibited. This can inhibit formation of the flow marks on the lateral wall of the can. Moreover, if the ending temperature is 550° C. or lower, the amount of the rolled textures to be subjected to the hot finishing rolling is increased.

The reduction ratio at a last pass in the hot rough rolling is preferably, for example, 5.0 to 40%. If the reduction ratio at the last pass is 5.0% or higher, the recrystallization when the rolling finishes is suitably controlled. As a result, a desirable amount of the rolled textures is subjected to the hot finishing rolling, inhibiting the 0-90° ears of the hot rolled sheet from becoming excessively high. Moreover, if the reduction ratio at the last pass is 5.0% or higher, the number of passes can be small and thus the productivity of the aluminum alloy sheet is improved.

If the reduction ratio at the last pass is 40% or lower, the progress of the recrystallization when the rough rolling finishes is inhibited. This causes an increase in amount of the rolled textures to be subjected to the hot finishing rolling, and thus causes an increase in height of the 0-90° ears of the hot rolled sheet.

The strain rate at the last pass in the hot rough rolling is preferably 5.0 to 30 s⁻¹. If the strain rate is 5.0 s⁻¹ or higher, the recrystallization when the rolling finishes is suitably controlled. Consequently, a desirable amount of the rolled textures is subjected to the hot finishing rolling, inhibiting the 0-90° ears of the hot rolled sheet from becoming excessively high. Moreover, if the strain rate is 5.0 s⁻¹ or higher, the rolling time can be limited and thus the productivity of the aluminum alloy sheet is improved.

If the strain rate is 30 s⁻¹ or lower, the progress of the recrystallization when the rough rolling finishes is inhibited. This causes an increase in amount of the rolled textures to be subjected to the hot finishing rolling, and thus causes an increase in height of the 0-90° ears of the hot rolled sheet. Accordingly, the flange length variation is reduced. The hot rough rolling can be performed with, for example, a reversing mill.

(5) Hot Finishing Rolling

The hot finishing rolling is intended for shaping the aluminum alloy sheet into a specific size. The structure of the aluminum alloy sheet after the hot finishing rolling finishes becomes a recrystallized structure due to its self-annealing.

In the hot finishing rolling, the tandem hot rolling machine, for example, can be used. With the tandem hot rolling machine, the number of passes can be reduced as compared to a case where the reversing mill is used. This can inhibit the recrystallization that takes place between passes, and thus the 0-90° ears of the hot rolled sheet can be sufficiently developed.

The ending temperature in the hot finishing rolling is preferably 300 to 400° C. If the ending temperature is 300° C. or higher, the rate of the recrystallization after the aluminum alloy sheet is cooled down to a room temperature can be further increased, and thus it is possible to inhibit a shortage of recrystallized grains in a cube orientation. If the ending temperature is 400° C. or lower, seizing and a rough surface can be inhibited, and thus the surface properties of the hot rolled sheet can be improved. As a result, the flow marks can be inhibited from being formed on the lateral wall of the can.

The total reduction ratio in the hot finishing rolling is preferably 80 to 95%. If the total reduction ratio is 80% or higher, the rolled textures are facilitated to gather. This increases a cube orientation density in the aluminum alloy sheet when the sheet is coiled up after the hot finishing rolling, and thus can reduce the 45° earing ratio. If the total reduction ratio is 95% or lower, the 0-90° ears of the hot rolled sheet can be inhibited from becoming excessively high. Moreover, if the total reduction ratio is 95% or lower, the surface properties of the hot rolled sheet is improved and thus the flow marks can be inhibited from forming on the lateral wall of the can.

(6) Cold Rolling

The cold rolling provides the aluminum alloy sheet with strength necessary for a can body. The reduction ratio in the cold rolling is preferably 80 to 90%. If the reduction ratio is 80% or higher, the strength of the aluminum alloy sheet can be further improved. Having the further improved strength, the aluminum alloy sheet can achieve sufficient buckling pressure for the DI formation.

If the reduction ratio is 90% or lower, it is less likely that the strength of the aluminum alloy sheet is excessively increased, and thus cracks due to a cupping processing and/or cracks in the can-bottom can be inhibited from occurring during the DI formation. Moreover, if the reduction ratio is 90% or lower, the 45° ears become low.

(7) Characteristics of Produced Aluminum Alloy Sheet

The aluminum alloy sheet produced according to the production method for an aluminum alloy sheet of the present disclosure has the following characteristics, for example.

(a) The 45° earing ratio of the cup formed by the first drawing of the aluminum alloy sheet is 2.0% or less.

(b) The value obtained by subtracting the 45° earing ratio from the 0-180° earing ratio of the cup, formed by the first drawing of the aluminum alloy sheet, is −1.0% or more and 2.0% or less.

(c) When the can height of the can body, formed of the aluminum alloy sheet by the DI formation and the necking formation, is measured along its entire circumference, the difference between the maximum value and the minimum value of the can height is preferably 0.080 mm or smaller. This difference between the maximum value and the minimum value is a variation in height of the neck in Embodiments to be described below.

The reason that the aluminum alloy sheet has the aforementioned characteristics is assumed to be as follows. The inventors of the present disclosure found out that the growth of the recrystallized grains in the cube orientation is facilitated in a process called “self-annealing” in which the post-hot-rolling recrystallization of the rolled textures, gathered in the middle of the hot rolling, is in progress. The above-described conditions for the ingot homogenizing treatment and for the hot rolling are conditions under which the rolled textures are easily developed by the hot rolling. According to the production method of the present disclosure, the rolled texture components are developed after the hot rolling and the density of the components in the cube orientation during the self-annealing is increased. Accordingly, the flange length variation can be reduced.

(8) Use of Aluminum Alloy Sheet

The aluminum alloy sheet according to the present disclosure can be intended for, for example, an aluminum alloy sheet for forming a can body by the DI formation. The aluminum alloy sheet according to the present disclosure may also be used for other purposes.

3. Embodiments

Embodiments of the present disclosure will be described more in detail below. It should be noted that the present disclosure is not limited to the embodiments.

(1) Production of Aluminum Alloy Sheet

Alloy components shown in Table 1 were used as raw materials so as to obtain Alloys (plate-shaped ingots) A to D with thicknesses of 500 mm by melting and casting, which are common methods. Subsequently, the surfaces of Alloys A to D were shaven to the thicknesses of 470 mm. As reference examples, Alloys E to L having different compositions of the raw materials were produced in the same manner as the aforementioned Alloys A to D.

TABLE 1 Alloy Si Fe Cu Mn Mg Al A 0.33 0.45 0.22 1.04 1.00 Bal. B 0.06 0.66 0.06 0.81 1.47 Bal. C 0.58 0.06 0.17 1.48 0.82 Bal. D 0.35 0.33 0.24 0.88 1.08 Bal. E 0.62 0.43 0.23 1.31 1.32 Bal. F 0.33 0.82 0.21 1.04 1.04 Bal. G 0.37 0.37 0.03 0.92 0.96 Bal. H 0.24 0.40 0.36 1.13 1.26 Bal. I 0.34 0.41 0.11 0.75 0.84 Bal. J 0.31 0.38 0.22 1.53 0.99 Bal. K 0.35 0.47 0.13 0.83 0.74 Bal. L 0.35 0.42 0.22 1.05 1.55 Bal.

Subsequently, using Alloys A to L, the homogenizing treatment, the hot rough rolling, the hot finishing rolling, and the cold rolling were sequentially performed.

The conditions for the homogenizing treatment, the hot rough rolling, the hot finishing rolling, and the cold rolling (hereinafter to be referred to as production conditions) are shown in Table 2. There are Production Conditions a to j. The following points are common to all the production conditions: the hot rough rolling was performed with a single-stand reversing mill that has work rolls with diameters of 930 mm; the hot finishing rolling was performed with a four-stand tandem rolling machine; and the cold rolling was performed in accordance with a common method.

TABLE 2 Homogenizing Hot Rough Rolling Hot Finishing Rolling Cold Rolling Treatment Ending Reduction Ratio Strain Rate Ending Total Total Production Temperature Time Temperature at Last Pass at Last Pass Temperature Reduction Ratio Reduction Ratio Conditions ° C. h (° C.) (%) (s⁻¹) (° C.) (%) (%) a 605 5.0 476 26.1  8.8 364 93.0 85.8 b 580 46.4 519 36.1 27.2 395 92.5 80.2 c 610 2.1 455 16.1  5.2 364 81.5 89.1 d 595 3.2 411 23.0  6.7 308 82.0 87.0 e 603 24.2 394 f 605 21.3 563 g 608 13.7 499 42.0 h 603 25.9 426 19.5 33.2 i 602 22.0 497 20.4 20.4 357 87.0 75.9 j 586 27.1 431 21.6 19.4 336 86.8 90.9

The strain rates at the last pass in the hot rough rolling shown in Table 2 are values determined by Formula (1).

$\begin{matrix} \left\lbrack {{Mathematical}\mspace{14mu} {Formula}\mspace{14mu} 1} \right\rbrack & \; \\ {{{Strain}\mspace{14mu} {Rate}\mspace{14mu} \left( s^{- 1} \right)} = \frac{v\; ɛ}{\sqrt{R\left( {t^{\prime} - t} \right)}}} & {{Formula}\mspace{14mu} (1)} \end{matrix}$

v in Formula (1) is a rolling rate (mm/s). The equivalent strain ε in Formula (1) is a value expressed by Formula (2).

$\begin{matrix} \left\lbrack {{Mathematical}\mspace{14mu} {Formula}\mspace{14mu} 2} \right\rbrack & \; \\ {{{Equivalent}\mspace{14mu} {Strain}\mspace{14mu} ɛ} = {{- \frac{2}{\sqrt{3}}}{\ln \left( {1 - \frac{r}{100}} \right)}}} & {{Formula}\mspace{14mu} (2)} \end{matrix}$

R in Formula (1) is the radius of the work rolls (mm). The sheet thickness t′ before the last pass in Formula (1) is a value expressed by Formula (3).

$\begin{matrix} \left\lbrack {{Mathematical}\mspace{14mu} {Formula}\mspace{14mu} 3} \right\rbrack & \; \\ {{{Sheet}\mspace{14mu} {Thickness}\mspace{14mu} t^{\prime}\mspace{14mu} {before}\mspace{14mu} {Last}\mspace{14mu} {Pass}} = \frac{t}{1 - \frac{r}{100}}} & {{Formula}\mspace{14mu} (3)} \end{matrix}$

t in Formula (1) and Formula (3) is the thickness (mm) of the sheet on the hot rough rolling side. r in Formula (3) is the reduction ratio (%) at the last pass.

Combinations of the type of alloy and the production condition are shown in Table 3. Different combinations of the type of alloy and the production condition make multiple production examples, which are Production Examples Nos. 1 to 24.

TABLE 3 45° (0-180° earing ratio) − Variation earing ratio (45° earing ratio) in Neck Height Ironing Buckling Surface No. Alloy Process (%) (%) (mm) Formability Pressure Properties 1 A a 0.7 1.0 0.033 ◯ ◯ ◯ 2 A b 0.5 0.7 0.040 ◯ ◯ ◯ 3 A c 1.3 −0.1  0.067 ◯ ◯ ◯ 4 A d 0.8 0.3 0.056 ◯ ◯ ◯ 5 B a 0.8 0.3 0.056 ◯ ◯ ◯ 6 C a 0.5 0.7 0.057 ◯ ◯ ◯ 7 D a 0.5 0.3 0.048 ◯ ◯ ◯ 8 B b 0.5 0.3 0.046 ◯ ◯ ◯ 9 C c 1.2 0.0 0.072 ◯ ◯ ◯ 10 D d 0.6 0.3 0.060 ◯ ◯ ◯ 11 E a 2.1 — — X ◯ ◯ 12 F a 0.8 0.4 0.041 X ◯ ◯ 13 G b 0.4 0.7 0.045 ◯ X ◯ 14 H b 0.2 0.8 0.051 X ◯ ◯ 15 I c 1.2 −0.3  0.062 ◯ X ◯ 16 J c 1.5 −0.5  0.065 X ◯ ◯ 17 K d 0.8 0.0 0.057 ◯ X ◯ 18 L d 0.6 0.3 0.052 X ◯ ◯ 19 A e 0.4 2.2 X ◯ ◯ 20 A f 2.3 — — ◯ ◯ X 21 B g 2.3 — — ◯ ◯ ◯ 22 B h 2.1 — — ◯ ◯ ◯ 23 C i 0.6 0.3 0.050 ◯ X ◯ 24 D j 2.3 — — X ◯ ◯

Cold rolled sheets having thicknesses of 0.29 mm were obtained by Production Examples Nos. 1 to 24. These cold rolled sheets correspond to the above-described aluminum alloy sheet.

(2) Evaluation of Aluminum Alloy Sheets

The earing ratio, the variation in neck height, the ironing formability, the buckling pressure, and the surface properties of the produced cold rolled sheets were evaluated. The evaluation method and the evaluation criteria are as follows.

(2-1) Earing Ratio

Specimen as blanks having diameters of 57 mm were subjected to deep-drawing by Erichsen Tester. The diameter of a punch was 33 mm, and R of the shoulder of the punch was 2.5 mm. The fold pressure was 300 kgf. The height of the obtained cups was measured at every 22.5° relative to the direction of rolling.

The 45° earing ratio and the 0-180° earing ratio were calculated by the following Formulas.

45° earing ratio (%)=(Average height of 45° positions−Average height)/Average height×100

0-180° earing ratio (%)=(Average height of 0° position and 180° position−Average height)/Average height×100

“Height of 45° positions” means the height of ears that are formed on a cup obtained by Erichsen Tester (to be referred to as Erichsen cup) and are located in the positions forming 45° angles relative to the rolling direction. “Average height of 45° positions” means the average value of “Height of 45° positions” that are located at four points of one cup. “Average height” means the average value of the height of the Erichsen cup at sixteen points obtained by measuring the cup at every 22.5° from the rolling direction. “Average height of 0° position and 180° position” means the average value of the height of two cup ears that are located in the positions at 0° and 180° from the rolling direction. “The positions forming 45° angles relative to the rolling direction” described above mean four positions respectively forming 45°, 135°, 225°, and 315° angles relative to the rolling direction.

(2-2) Neck Height Variation

Circular sheets as blanks having diameters of 140 mm were subjected to the DI formation so as to form cans having can-bodies with inside diameters of 66 mm. Subsequently, the ears at opening portions of the cans were trimmed. Then, the cans were subjected to the necking formation in a way that the inside diameters thereof became 57 mm. The height of the cans after the necking formation were measured at every 22.5°. The aforementioned diameters of the blanks, the inside diameters of the can-bodies, and the inside diameters of the necks were determined based on the shapes of can-bodies that were generally used within Japan. The difference between the maximum value and the minimum value of the average of the height of positions at 0°, 22.5°, 45°, 67.5°, and 90° was defined as the neck height variation. The neck height variation is an indicator for the flange length variation. The neck height variation is preferably 0.080 mm or shorter.

(2-3) Ironing Formability

Circular sheets as blanks having diameters of 140 mm were subjected to the DI formation so as to form cans with inside diameters of 66 mm. Then, intensive ironing formation tests were run, in which cutoff of the cans were forcibly caused, using a punch that makes the outside diameters of the cans increased from the bottoms toward the opening portions. From the average value of the thicknesses of the lateral walls of the cans, which were obtained when the cutoff was caused in the tests for ten cans, a limiting ironing ratio was calculated based on the following Formula. The limiting ironing ratio is an indicator for the ironing formability.

Limiting ironing ratio (%)=(Original sheet thickness−Thickness of lateral wall of can when being cut off)/Original sheet thickness×100

In Table 3, the limiting ironing ratios of 46% or more were determined to be ◯. Moreover, in Table 3, the limiting ironing ratios of less than 46% or production examples that were unable to form cans due to an occurrence of cracks caused by the cupping processing and/or cracks in the can-bottom during the DI formation were determined to be X.

(2-4) Buckling Pressure

The cans formed by the DI formation were baked at 200° C. for 20 minutes. Subsequently, the pressure that caused buckling of the bottoms of the can materials which had been formed into dome shapes was measured by a pneumatic pressure resistance tester. In Table 3, cans resistant to pressure of 6.0 kgf/cm² or more were determined to be ◯, and production examples resistant to pressure of less than 6.0 kgf/cm² were determined to be X.

(2-5) Surface Properties

The intensity of the flow marks on the produced cold rolled sheets was visually evaluated. Production examples on which no defect was visually observed were determined to be ◯, while production examples on which defects were visually easily observed were determined to be X.

Evaluation results on each of the points are shown in the aforementioned Table 3.

In Production Examples Nos. 1 to 10, all of the earing ratio, the neck height variation, the ironing formability, the buckling pressure, and surface properties were determined to be good. The aluminum alloy sheets produced in Production Examples Nos. 1 to 10 had suitable textures.

The aluminum alloy sheets produced in Production Examples Nos. 1 to 10 have small flange length variations, and thus the seaming of the cans with the can-lids can be performed well. Moreover, the aluminum alloy sheets produced in Production Examples Nos. 1 to 10 have desirable characteristics for can bodies in terms of the buckling pressure, the ironing formability, the surface properties, and so on. Production Examples Nos. 1 to 10 can be easily achieved through a common method by limiting the hot rolling condition and so on. Thus, Production Examples Nos. 1 to 10 achieve industrially significant effects.

In Production Example No. 11, the excessive amount of Si caused a reduction of the recrystallization rate of the hot rolled sheet and rendered the strength high, resulting in deterioration in ironing formability. Moreover, the 45° earing ratio was high, and the neck height variation was large.

In Production Example No. 12, the excessive amount of Fe caused formation of large crystals, resulting in deterioration in ironing formability of the cans.

In Production Example No. 13, the shortage in amount of Cu caused low strength of the alloy sheet, resulting in deterioration in buckling pressure of the cans.

In Production Example No. 14, the excessive amount of Cu caused an excessive increase in strength of the alloy sheet, resulting in deterioration in ironing formability of the cans.

In Production Example No. 15, the shortage in amount of Mn caused a lack of strength of the alloy sheet, resulting in deterioration in buckling pressure of the cans.

In Production Example No. 16, the excessive amount of Mn caused an excessive increase in strength of the alloy sheet, resulting in poor ironing formability of the cans.

In Production Example No. 17, the shortage in amount of Mg caused a lack of strength of the alloy sheet, resulting in deterioration in buckling pressure of the cans.

In Production Example No. 18, the excessive amount of Mg caused an excessive increase in strength of the alloy sheet, resulting in poor ironing formability of the cans.

In Production Example No. 19, since the ending temperature of the hot rough rolling became too low, the finish rolling was performed while many rolled textures were still remaining in the alloy sheets. This caused an excessive increase in cube orientation density and rendered the 0-180° ears of the final sheet too high, resulting in multiple tear-offs in the ironing.

In Production Example No. 20, since the ending temperature of the hot rough rolling became too high, the recrystallization when the rough rolling finished became too progressive. Accordingly, the finish rolling was performed while the degree of gathering of the rolled textures was still low. This caused a low cube orientation density, a high 45° earing ratio of the final sheet, and a large neck height variation. Moreover, the surface quality of the hot rolled sheet was poor, and the flow marks appeared on the can surfaces.

In Production Example No. 21, since the reduction ratio at the last pass in the hot rough rolling was too high, the recrystallization when the rough rolling finished became too progressive. Accordingly, the finish rolling was performed while only a small amount of strain had been accumulated. This resulted in a low cube orientation density, a high 45° earing ratio of the final sheet, and a large neck height variation.

In Production Example No. 22, since the strain rate at the last pass of the hot rough rolling was too high, the recrystallization when the rough rolling finished became too progressive. Accordingly, the finish rolling was performed while only a small amount of strain had been accumulated. This resulted in a low cube orientation density, a high 45° earing ratio of the final sheet, and a large neck height variation.

In Production Example No. 23, since the total reduction ratio in the cold rolling was too low, the strength of the alloy sheet was low, and thus the buckling pressure of the cans was decreased.

In Production Example No. 24, since the total reduction ratio in the cold rolling was too high, the strength of the alloy sheet was high, and thus the ironing formability of the cans was deteriorated. Moreover, the 45° earing ratio of the final sheet was high, and the neck height variation was large.

The above has described embodiments of the present disclosure. Nevertheless, the present disclosure is not limited to the above-described embodiments and can be modified in various forms.

(1) A function of a single component in each of the aforementioned embodiments may be distributed to a plurality of components; functions of a plurality of components may be achieved by a single component. A part of the configuration of each of the aforementioned embodiments may be omitted; at least one part of the configuration of each of the aforementioned embodiments may be added to or altered with the configuration of another embodiment or other embodiments of the aforementioned embodiments. All the modes that are encompassed in the technical ideas defined by the language in the claims are embodiments of the present disclosure.

(2) In addition to the above-described aluminum alloy sheet, the present disclosure can be carried out in various forms such as a can body formed by the DI formation using the aluminum alloy sheet, a production method for a can body formed by the DI formation, and so on. 

1. An aluminum alloy sheet comprising: 0.05 to 0.60% by mass of Si; 0.05 to 0.80% by mass of Fe; 0.05 to 0.25% by mass of Cu; 0.80 to 1.50% by mass of Mn; 0.80 to 1.50% by mass of Mg; Al; and inevitable impurities, wherein a 45° earing rate of a cup formed by a first drawing of the aluminum alloy sheet is 2.0% or less, and wherein a value obtained by subtracting the 45° earing rate from a 0-180° earing rate of the cup formed by the first drawing of the aluminum alloy sheet is −1.0% or more and 2.0% or less.
 2. A production method for an aluminum alloy sheet comprising: homogenizing treatment of an aluminum alloy ingot including 0.05 to 0.60% by mass of Si, 0.05 to 0.80% by mass of Fe, 0.05 to 0.25% by mass of Cu, 0.80 to 1.50% by mass of Mn, 0.80 to 1.50% by mass of Mg, Al, and inevitable impurities; hot rough rolling of the aluminum alloy ingot with a reversing mill under a condition where: an ending temperature is 400 to 550° C.; a reduction ratio at a last pass is 5.0 to 40%; and a strain rate at the last pass is 5.0 to 30 s⁻¹, hot finishing rolling of the aluminum alloy ingot with a tandem hot rolling machine; and cold rolling of the aluminum alloy ingot under a condition where the reduction ratio is 80 to 90%.
 3. The production method for an aluminum alloy sheet according to claim 2, wherein the homogenizing treatment is performed at a temperature of 580 to 610° C. for 2 to 48 hours.
 4. The production method for an aluminum alloy sheet according to claim 2, wherein an ending temperature in the hot finishing rolling is 300 to 400° C., and wherein a total reduction ratio in the hot finishing rolling is 80 to 95%.
 5. The production method for an aluminum alloy sheet according to claim 2, wherein the aluminum alloy sheet according to claim 1 is produced. 